Light-Harvesting "Antenna" Behavior In Nu-1000

Structural or conceptual synthetic analogues of natural photosynthetic light-harvesting complexes hold promise as entities capable of both efficient collection of visible-region solar photons and rapid and efficient delivery of stored solar energy to energy-converting electrodes or chemical catalysts. Porous, crystalline metal-organic frameworks (MOFs) are promising supramolecular scaffolds for this purpose. Here, we report on the "antenna behavior" of chromophore assemblies comprising aligned organic linkers within a zirconium-based MOF, NU-1000. The behavior was probed primarily via amplified emission quenching using either an electron donor (ferrocene carboxylate) or an electron acceptor (3,5-dinitrobenzoate) as a redox quencher. We used solvent-assisted ligand incorporation (SALI) as a versatile means of siting/immobilizing desired quencher molecules directly within the extended chromophoric structures. We find that a photogenerated molecular exciton (spanning about four linkers) can sample similar to 300 chromophoric linkers.behavior which translates to a single-step energy-transfer or exciton-hopping time of a few picoseconds. These findings clearly suggest that NU-1000 and similar MOFs can offer an "antenna" of significant size and that with a suitable catalyst immobilized on the MOF node, can find application in solar energy conversion devices.